The subject disclosure relates to evaluation of mineralogy and organic content of earth materials. The mineralogy of an earth formation surrounding a borehole is valuable to determining whether it is feasible and cost efficient to produce hydrocarbons from the borehole in question.
There are a number of techniques in the oil industry to perform quantitative mineral analysis of an earth formation. In each case, core samples are extracted from the borehole and are used to represent the formation at different depths.
Infrared spectroscopy, particularly Fourier transform infrared (FTIR) spectroscopy, has been used to analyze the mineral composition of rock samples. Typically, a portion of the core sample is ground up and added to a carrier such as potassium bromide (KBr). The mixture is then formed into a pellet through a series of grinding and dispersing steps. The pellet is pressed and weighed to account for lost material. Finally, the pellets are irradiated with infrared radiation in an FTIR spectrometer and a spectral response signal is obtained representative of the infrared radiation absorbed by the sample. The frequency and amplitude of each characteristic spectral response can be obtained. Comparison is made in the spectrum for the sample with spectra for standard minerals to determine a quantitative measure of the minerals in each sample. Many of the approaches in transmission FT-IR are used in the subject disclosure with reflection FT-IR, including the analysis of whole and powdered mineral standards that have been chemically assayed for purity.
X-ray fluorescence (XRF) spectrometers have been used to analyze the chemical composition of rock samples. In X-ray fluorescence (XRF) spectrometers, the chemical composition of a substance is determined by irradiating the sample under test with X-rays and by recording the secondary X-ray fluorescent radiation emitted by the sample.
Handheld X-ray fluorescence (XRF) analyzers are commercially available from many companies. These analyzers are calibrated for some specific applications, but they appear to need calibration/optimization in order to provide robust measurements for common sedimentary earth materials; an example of how this calibration may be performed is provided by Kenna et al., entitled “Evaluation and calibration of a field portable X-ray fluorescence spectrometer for quantitative analysis of siliciclastic soils sediments,” Journal of Analytical Atomic Spectrometry, 2010. Such analyzers have been incorporated into core scanning systems, for example, the GEOTEK multi-sensor core logger.